The branch of the Celtic language which includes Welsh, Cornish, Breton, and the extinct languages of Gaulish, Lepontic, Noric, and Galatian. Unlike the Q-Celtic branch, the P-Celtic employs the use of the letter "p" where the Q branch often uses a "k" sound.

Breton and Cornish are closely related, and Breton is usually classified as an insular language, as the Bretons were originally refugees from Britain, and not Gauls.

Some argue that the Q-Celtic branch is older; however, Lepontic inscriptions have been found in North Italy, and date to 700 BCE. Of course, others have argued that Lepontic isn't Celtic, but Ligurian, another Indo-European language system of Italy.